This invention generally relates to a technology for automatically determining the heat-conductive properties of print media.
Laser printers (such as the one shown at 100 in FIG. 1) and copiers are common examples of electrophotographic production devices. In general, the art of electrophotographic production devices (EPD) is well known. The focus, herein, is on one component of EPDs: the registration assembly, Traditionally, the role of the registration assembly is to deskew (i.e., straight) the print medium before an image is printed on it.
The following U.S. patents include a general description of an EPD and/or the role of the registration assembly of such a device: U.S. Pat. Nos. 5,865,121; 6,201,937; and 5,967,511.
Herein, references to laser printers (like printer 100 in FIG. 1) expressly include all EPDs. Also, references to print media, herein, generally refers to paper on which images are printed, but it may include other substrates, such as acetate.
Just before the print medium passes through the imaging area, the printer stops the medium at an internal portion of the printer called the xe2x80x9cregistration assembly.xe2x80x9d In the registration assembly, a movable xe2x80x9cstopxe2x80x9d pops up and literally stops the progress of the medium through the printer. The printer grabs the leading edge of the paper and deskews it (i.e., squares it up). The registration assembly is responsible for ensuring that the paper travels straight into the fuser unit of the printer.
The fuser unit of a laser printer heats the print medium and the toner on the medium as it passes through it. The typical operating temperature of a fuser unit is about 190xc2x0 Celsius, but it may be adjusted. The goal of the fuser is to thoroughly melt the toner onto the medium. After it leaves the fuser unit, the toner should be firmly affixed to the medium.
To optimize performance, the fusing of the toner to the medium should occur as quickly and efficiently as possible. However, if the toner is not thoroughly melted onto the medium, the tonerxe2x80x94which is typically in the form of an extraordinarily fine powderxe2x80x94tends to rub off easily.
Time and temperature play a vital role in fusing toner onto print media. If the time taken for the medium to pass through the fuser is too long, the medium can be damaged or the printed image might deteriorate. If the time is too short, the toner may not properly adhere to the medium. Similarly, if the temperature is too high, the medium can be damaged or the printed image might deteriorate. If the temperature is not high enough, the toner may not properly adhere to the medium.
All materials have heat conductive properties. The most common print media, by far, is paper. However, paper is a fairly good insulator. It does not conduct heat extremely well. Thicker paper generally doesn""t conduct heat as well as thinner paper.
As it passes through a fuser unit, thin paper transfers the heat quickly to the toner; therefore, the toner melts and adheres quickly. Thicker paper will transfer the heat slower; therefore, greater time or temperature is necessary for the toner to fully adhere.
Since heat transfer is slower with heavy paper, the following may be done to insure that the toner is sufficiently affixed to the paper: slow the paper down as it passes through the fuser unit and/or increase the temperature in the fuser unit.
The printing process can be tuned so the toner can be firmly affixed to the medium. Knowing the thickness of the medium gives a measure of heat conductivity, which can be used to tune the printing process. The speed of the paper in the paper path, and/or the temperature of the fuser can be adjusted so the toner is affixed and the medium is not damaged.
To expand their market appeal, printer manufacturers prefer that their printers are versatile and accommodate a wide variety of print media. For example, it is desirable for the printer to accommodate a range of print media from very thin, lightweight paper to very thick, heavy paper.
It is advantageous for the characteristics of the paper to be known before printing so that the printer can adjust accordingly. The typical objective is to get the toner to fully adhere to the medium.
To accommodate a range of print media thicknesses, printer manufacturers have taken three conventional approaches: Limited media thickness support, poor fusing performance, and/or manual fuser temperature control.
Limited Media Thickness Support
By specification, some manufacturers narrowly limit the range of media thickness, or media weight, supported by their printers. These printers have a configuration of temperature and media transfer speed that achieves optimal toner affixation with the specified, narrow, range of media thicknesses. Typically, this range includes the thickness of media most commonly employed. Thus, the specification limits the range of media thickness supported by the printer. For example, the specification may indicate that cardstock, a heavy, thick medium, is not supported for the printer.
In a traditional office environment, this narrow thickness range is sufficient for most applications. However, printers with this narrow media thickness specification have little or no appeal to markets where a wider variety of media is commonly used.
Poor Fusing Performance
Some manufacturers have expressly enlarged the range of supported thicknesses, but have done nothing to solve the problems discussed above. Although the manufacturers know that there is a problem with toner affixation with thick media, such media is still expressly supported. This approach does not solve the problems discussed abovexe2x80x94rather, it simply ignores the problems.
Manual Fuser Temperature Control
In some instances, the users are given manual fuser temperature control to accommodate thicker or heavier print media. Such control may be via a control panel on the printer or via user interface on a computer. In response to the user""s input about the media""s thickness, the printer adjusts the temperature of the fuser unit or the speed at which the paper passes through the fuser unit.
Of course, like most manual controls, there is room for problems with this approach. Most users will not be aware of this existence of the manual control capability nor will they appreciate its importance. Moreover, there is a great chance of error. The user may erroneously specify a different thickness for the media than what is actually used. Someone else may change media, but the printer is still configured to print to a media of a different thickness.
Accordingly, there is a need for automatic determination of the thickness of a print medium so that the printing process may be adjusted automatically to achieve optimum results.
Described herein is a technology for automatically determining the heat-conductive properties of print media. More particularly, described herein is a technology for indirectly and automatically determining the heat-conductive properties of print media by determining the stiffness of print media, such as acetate and paper.
At least one embodiment, described herein, includes a registration assembly of a laser printer. In this assembly, the print medium is deflected (i.e., bent, bowed, buckled, etc.). A measurement of such deflection is made. That measurement is an indication of the relative stiffness of the print medium. Assuming approximately similar densities, the stiffness of print media is directly related to its thickness. The thicker the medium the stiffer it is and vice versa. The thickness of print media is directly related to its heat conductivity.
By measuring the relative stiffness of a print medium, the toner fusing process may be adjusted based upon the relative heat conductive properties of the print medium. For example, the fuser temperature may be adjusted or the paper processing speed may be adjusted.
This summary itself is not intended to limit the scope of this patent. Moreover, the title of this patent is not intended to limit the scope of this patent. For a better understanding of the present invention, please see the following detailed description and appending claims, taken in conjunction with the accompanying drawings. The scope of the present invention is pointed out in the appending claims.